RFR: 8355563: VectorAPI: Refactor current implementation of subword gather load API

[Emanuel Peter]

On Fri, 30 May 2025 08:15:22 GMT, Xiaohong Gong <xgong at openjdk.org> wrote:

>>> @XiaohongGong Thanks for splitting this one out, and for investigating the regressions here.
>>> 
>>> Putting the permalink here, fixed to the current change (the link you pasted will always refer to the newest, which may later on point to the wrong line when lines above are inserted / deleted):
>>> 
>>> https://github.com/openjdk/jdk/blob/7077535c0b0a6ea0a2a167f9135b1504a3d71fb3/src/hotspot/share/opto/loopnode.cpp#L1659-L1661
>>> 
>>> I wonder if we should just use `Node::uncast` there? But I'm quite unsure about that.
>> 
>> Sounds good to me. I will have a deep investigation for it. Thanks!
>> 
>> 
>> 
>>> > Yes, I also observed such regression.
>>> > It would be nice if you proactively mentioned regressions, so it does not have to be pointed out by reviewers.
>>> 
>>> For me, it could be ok to fix it in a follow-up patch. I think we are too close to RDP1 for JDK25 now anyway, and so we could push this patch here into JDK26, and then we have enough time in JDK26 to investigate the regression. Even better would be if we could do the other patch first, so we never even encounter a regression.
>> 
>> Sounds good to me. Thanks!
>
>> > @XiaohongGong Thanks for splitting this one out, and for investigating the regressions here.
>> > Putting the permalink here, fixed to the current change (the link you pasted will always refer to the newest, which may later on point to the wrong line when lines above are inserted / deleted):
>> > https://github.com/openjdk/jdk/blob/7077535c0b0a6ea0a2a167f9135b1504a3d71fb3/src/hotspot/share/opto/loopnode.cpp#L1659-L1661
>> > 
>> > I wonder if we should just use `Node::uncast` there? But I'm quite unsure about that.
>> 
>> Sounds good to me. I will have a deep investigation for it. Thanks!
> 
> Hi @eme64  @jatin-bhateja,  I'v created a PR https://github.com/openjdk/jdk/pull/25539 to fix this issue. With this change, the performance regression can be fixed as well.  Could you please take a look at that change and help to run the test on different X86 machines?   Thanks a lot!

@XiaohongGong I reviewed https://github.com/openjdk/jdk/pull/25539. Since it is a relatively simple patch, I suggest that we integrate that one first, and come back to this here later. Is that ok for you?

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PR Comment: https://git.openjdk.org/jdk/pull/25138#issuecomment-2930007655